Technical Field
The present invention relates to conversion between a microwave and an optical domain and, more particularly, to a transducer to convert single-photon microwave signals to optical signals.
Description of the Related Art
Various communication protocols rely on optical fibers because of their low loss, high bandwidth, low background noise, and the ease of routing. Optical fibers can also be used for sending quantum information in the form of single photons or coherent states. On the other hand, many viable quantum processing architectures operate at microwave frequencies. The high amplitude stability of microwave structures allows precise controls on quantum bits (qubits) that enable high-fidelity gate operations. However, microwave photons are more difficult to use for long-range communication purposes, due to high thermal background noise and high loss when such signals propagate in waveguides.
Existing approaches to converting between microwave signals and optical signals are complicated, difficult to implement in solid state systems, or difficult to optimize. Some existing transducers use electro-optic crystalline optical resonators to perform microwave-to-optical conversion. One of the problems of using such resonators is that other coexisting non-linear properties, such as pyro-electricity and piezo-electricity, impede the microfabrication processes of the microwave resonator. Another problem is that microfabrication can likewise contaminate the crystalline electro-optic optical resonators and reduce the quality factor. These resonators also have a high microwave loss and are difficult to align at cryogenic temperatures.